A known apparatus for making coffee or other infusion beverages comprises a water supply container, an electrically heated water through-flow passage for carrying water from the supply container and thereby heating the water to produce steam which is passed through the coffee or the like for infusion thereof. A control means is disposed between the container and the passage for regulating the through-flow of water and for preventing steam from flowing back into the water supply container. In one form of this apparatus the control means for regulating the water through-flow and for preventing steam from flowing back into the water supply container comprises a valve with a movable valve member, generally a valve ball. This apparatus necessarily has a discontinuous mode of operation. Thus, when the water supply container has been filled, water flows through the valve by way of a feed conduit and into the electrically heated water through-flow passage and from there into a riser pipe. The outlet of the riser pipe, which is disposed for example above a coffee filter, is at a somewhat higher level than the maximum level of water in the water supply container, so that the flow into the riser pipe stops when the level of water in the riser pipe has reached the same level as the water in the supply container. The water is heated in this region, to a temperature which is close to boiling point, by the electrical heating means in the water through-flow passage, the outer layers of the column of liquid in the passage being converted into steam. Now, the increase in volume caused by the water being turned into steam results in a rise in the level of the column of liquid in the riser pipe and in the supply conduit connected to the supply container. The back-flow of water towards the supply container causes the ball valve to close so that a further increase in volume must necessarily take its effect in the riser pipe, so that first hot water and then water mixed with steam issues from the outlet opening of the riser pipe. If a large part of the column of water is discharged from the riser pipe and the water through-flow passage, the pressure in the passage collapses, as the steam can now escape substantially freely by way of the riser pipe. If the pressure in the passage drops below the pressure exerted by the standing column of liquid in the supply container, the ball valve opens and a fresh quantity of water can flow into the passage. The cold water flowing into the passage results in a cooling action and absorption of the steam so that the passage and the riser pipe are almost completely refilled with water. This procedure is then repeated, at approximately the same periods of time.
This mode of operation suffers from a number of serious disadvantages. Firstly, a not inconsiderable part of the water introduced into the water supply container is converted into steam which issues uselessly from the discharge opening of the riser pipe. If it is assumed that about one sixth of the water is converted into steam, the increased energy required is more than 30%, as the quantity of water must in fact first be heated to boiling point and then converted into steam. In addition, the steam issuing from the discharge opening of the riser pipe produces an unpleasant snorting noise. Furthermore, as the valve must necessarily include a movable member, the liability to breakdown of the apparatus is increased, whether this is due to jolts or being dropped or whether it is due for example to fouling as a result of incorrect use. Yet again, it is not possible to achieve the optimum water discharge temperature, by virtue of the discontinuous mode of operation. However, optimum discharge temperature of the water is of particular significance, more especially in the preparation of coffee. Furthermore, as apparatus of the above-indicated kind are generally mass-produced articles, the costs involved in producing the ball valve also play a not inconsiderable part.